In an apparatus for recording color pictures of colored printed matter or a color copy machine, a colored document is optically read with its colors being separated and converted into color recording signals (e.g. a toner signal) for color toners, color inks, or ink donor films, etc., and are supplied to a memory. In color masking, the color separating signals B (blue), G (green), and R (red) are subjected to the matrix operation shown below and are converted into Y (yellow), M (magenta), and C (cyan), respectively. ##EQU1##
By performing the above process, the color tone is controlled and the saturation of the colors is enhanced during the color reproducing process while the color balance is maintained.
With devices for forming and processing the color pictures as well as copy machines for recording the color pictures, conventionally, the signals B, G, and R, and signals Y, M, and C are subjected to END (Equivalent Neutral Density) conversion so as to facilitate the process. The color signals indicative of gray have a relation B=G=R (Equivalent Neutral Density), and supplying signals with the relation of Y=M=C will also reproduce gray. The recording signals Y, M, and C, which are converted through color masking and represented in terms of END converted signals, are processed as the density signals of the coloring materials of the toner or ink for printing. Through black production and under color removal processes, the coloring materials Y, M, C, and K (black or india ink) are efficiently mixed, thereby improving color tone reproducibility and saving coloring materials.
The color separating signals are often influenced by the spectrum of the light source for lighting, characteristics of the photoelectric transducers, the color filters, and the lenses. Also, the recording unit has factors that since the coloring materials used for recording the color images have unwanted absorption in their spectral property, a variety of characteristics are necessary to be corrected if preferable pictures cannot be obtained due to deviations in saturation and hue.
Moreover, there are many other factors such as papers, the characteristics of the color inks, which influence the reproducibility of degradation. For this reason, it is extremely difficult to faithfully reproduce the hue of the documents by simply processing color conversion.
Thus, data processing for the color picture includes END conversion, TRC (Tone Correction Control), and other processes in addition to the described color masking and the UCR (Under Color Removal) so as to reproduce the color of the document accurately.
For example, the color separating signals are read in the form of signals B, G, and R from the document. When a gray document (non-saturated color) is read, the separated color signals B, G, and R may not be of the same value due to variations of various characteristics and other conditions of the color-reading apparatus. Therefore, END conversion is applied to convert the color signals B, G, and R into signals having gray density of the same value. In the meantime, although the gray signal in which Y, M, and C are of the same value is outputted, the gray may not be faithfully reproduced due to the characteristics of the coloring materials and environmental conditions of the recording unit. Thus, TRC is performed to reproduce the gray color corresponding to the density of the recording signals Y, M, and C when these signals are of the same value.
Color masking is performed to convert the color separating signals into the recording signals Y, M, and C. At that time, a problem arises in how the colors (hue, saturation, etc.) other than gray are to be reproduced. In other words, END conversion, the color masking, and the TRC play important roles in reproducing of the colors including gray of the document.
As mentioned above, with a color picture recording apparatus, the END conversion process is carried out to perform color correction as well as control of correction of the color tone while maintaining gray balance and degradation, thereby reproducing the color pictures that exhibit good characteristics of tone, fineness, and granularity of the colors. That is, color correction is carried out on the basis of gray and then the recording signals Y, M, and C of the same amount are subtracted (under color removal) from the recording signals obtained through the color correction so as to eliminate unnecessary consumption of the color materials as well as to enhance producibility of the color. However, in reality, reproducing gray and black and reproducing colors of high degrees of saturation are in conflict with each other; therefore there is a problem that simple UCR process is not enough to enhance reproducibility of the color. Moreover, if UCR is performed, the amount of coloring materials will become small, causing a loss of color depth in the entire color picture.
To compensate for the lack of color depth or to output gray, black or india ink (K) is produced in accordance with the amount of color materials that are subjected to under color removal. However, in this case too, K causes a problem of muddiness in the saturated color and unfavorably influences reproducibility of the color tone. Moreover, under color removal processing requires large scale processing circuits.